Silicon photonics uses silicon as an optical medium and has been an active development area in recent years because of its potential monolithic integration with complementary-metal-oxide-semiconductor (CMOS) microelectronic circuits. Silicon is transparent to infrared light with wavelengths above about 1.1 μm and also has a very high refractive index of, for example, about 3.5. The tight optical confinement provided by this high refractive index allows for optical waveguides.
For silicon photonic components, e.g., waveguides and the like, to remain optically independent from the bulk silicon of the semiconductor wafer on which they are fabricated, it is necessary to have a layer of intervening material. Typically silica is used as an intervening material because of its much lower refractive index, about 1.44 in the wavelength region of interest, than silicon and thus, light at the silicon-silica interface will undergo total internal reflection and remain in the silicon. This construction is known as silicon-on-insulator (SOI) and the waveguides formed from this construction are commonly referred to as SOI waveguides. As such, silicon photonic devices can be made using existing semiconductor fabrication techniques, and because silicon is used as the substrate for most integrated circuits, it is possible to create hybrid devices in which the optical and electronic components are integrated onto a single microchip.
Because of their compatibility with CMOS technology, p-i-n germanium (Ge)-based photodetectors have also drawn much attention. P-i-n Ge photodetectors exhibit good responsivity and quantum efficiency for optical absorption. Integrating p-i-n Ge photodetectors onto SOI waveguides offers the advantage of low junction capacitance, efficient power transferring from the waveguide to the Ge photodetector, and ease of process integration. Unfortunately, current p-i-n Ge photodetectors integrated on SOI waveguides typically result in large topographical variation and optical mode proximity to the p-i-n electrodes and associated contacts, resulting in process complexity, high loss, and reduced optical sensitivity.
Accordingly, it is desirable to provide semiconductor devices including photodetectors integrated on waveguides with reduced topographical variation and methods for fabricating such semiconductor devices. Moreover, it is desirable to provide semiconductor devices including photodetectors integrated on waveguides with reduced loss and improved optical sensitivity. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.